OFFSET
0,13
COMMENTS
LINKS
T. D. Noe, Table of n, a(n) for n=0..5050
EXAMPLE
5 = 3 + 1 + 1, so a(5) = 1.
MAPLE
A063993 := proc(n)
local a, t1idx, t2idx, t1, t2, t3;
a := 0 ;
for t1idx from 1 do
t1 := A000217(t1idx) ;
if 3*t1 > n then
break;
end if;
for t2idx from t1idx do
t2 := A000217(t2idx) ;
if t1+t2 > n then
break;
end if;
t3 := n-t1-t2 ;
if t3 >= t2 then
if isA000217(t3) then
a := a+1 ;
end if;
end if ;
end do:
end do:
a ;
end proc: # R. J. Mathar, Apr 28 2020
MATHEMATICA
a = Table[ n(n + 1)/2, {n, 1, 15} ]; b = {0}; c = Table[ 0, {100} ]; Do[ b = Append[ b, a[ [ i ] ] + a[ [ j ] ] + a[ [ k ] ] ], {k, 1, 15}, {j, 1, k}, {i, 1, j} ]; b = Delete[ b, 1 ]; b = Sort[ b ]; l = Length[ b ]; Do[ If[ b[ [ n ] ] < 100, c[ [ b[ [ n ] ] + 1 ] ]++ ], {n, 1, l} ]; c
PROG
(Haskell)
a063993 n = length [() | let ts = takeWhile (< n) $ tail a000217_list,
x <- ts, y <- takeWhile (<= x) ts,
let z = n - x - y, 0 < z, z <= y, a010054 z == 1]
-- Reinhard Zumkeller, Jul 20 2012
(PARI) trmx(n)=my(k=sqrtint(8*n+1)\2); if(k^2+k>2*n, k-1, k)
trmn(n)=trmx(ceil(n)-1)+1
a(n)=if(n<3, return(0)); sum(a=trmn(n/3), trmx(n-2), my(t=n-a*(a+1)/2); sum(b=trmn(t/2), min(trmx(t-1), a), ispolygonal(t-b*(b+1)/2, 3))) \\ Charles R Greathouse IV, Jul 07 2022
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
N. J. A. Sloane, Sep 18 2001
EXTENSIONS
More terms from Robert G. Wilson v, Sep 20 2001
STATUS
approved